The present invention relates generally to heat sinks for electronic components and more particularly to a heat sink assembly of the kind that utilizes a spring that presses on one side of a multi-heat sink module to urge individual heat sinks to make good thermal contact with corresponding electronic components, such as integrated circuit chips.
Modern electronic appliances such as computers have many hundreds of integrated circuits and other electronic components, most of which are mounted on printed circuit boards. Many of these components generate heat during normal operation. Components that are relatively big or that have a relatively small number of functions in relation to their size, as for example individual transistors or small-scale integrated circuits, usually dissipate all their heat without a heat sink. The large physical sizes of such components, especially as compared with their active portions, limits their density on a circuit board sufficiently that there is enough room for any heat sinks that may be needed. Accordingly, any component that needs assistance in dissipating heat, regardless of size can have a heat sink of its own.
The term “heat sink” as used herein generally refers to a passive device, for example an extruded aluminum plate with a plurality of fins, which is thermally coupled to an electronic component to absorb heat from the component. The heat sink dissipates this heat into the air by convection.
One widely used method of increasing the speed of an electronic circuit is to reduce the lengths of the connecting wires. In part, this is accomplished by abandoning the older practice of enclosing each integrated circuit chip in a separate package in favor of mounting many chips next to each other on a single substrate. Such an assembly of chips and substrate is commonly referred to as a multi-chip module (“MCM”). However, since the chips are typically not all identical, the upper surface of this chips are not necessarily coplanar. In addition, the space required by the mounting hardware for an individual heat sink usually requires through holes in the printed circuit board. This negatively impacts routed traces in the area around the component being cooled by a heat sink. Another known heat sink system uses multiple springs to maintain the appropriate compressive force to maintain the required thermal bond between the heat sink and an upper surface of a chip or other component on the substrate.
It is also well known to attach a chip or other component to a heat sink with thermal paste or some other thermal interface material. However, the chips often are not all the same height above the substrate, for example because the chips themselves are of different thicknesses or because of variations in solder bump height or in flatness of the substrate. To compensate for these variations in height, a relatively thick layer of paste or other material must be used. The thermal conductivity of a given thermal interface material is not as good as that of solder, and the result is inadequate heat transfer when high-power chips are involved, for example.
There have been many attempts to solve the problem of dissipating heat developed by high-power integrated circuit chips in an MCM. Some of these solutions are mechanically complex, or are expensive, or make it difficult or impossible to rework or service the MCM. For these and other reasons, none of the prior approaches has adequately solved the problem. From the foregoing it will be apparent that there is still a need for a way to adequately dissipate heat from all the integrated circuit chips (or other components) in an MCM, for example. There is especially a need in the prior art for providing heat sinks for thermal components wherein there is a co-plurality tolerance between multiple packages (such as integrated circuit chips, heat producing components, etc.) on a printed circuit board assembly and wherein there may be limited mounting space on densely populated printed circuit boards.